Research to-date has generated only abnormally functioning insulin-expressing cells, which do not secrete appropriate amounts of insulin in response to sequentially varied glucose levels, or pancreatic progenitor cells that can only mature into functioning insulin-expressing cells after 3 months of transplantation into a mouse host (Cheng et. al., 2012; D'Amour et al., 2005; D'Amour et al., 2006; Kroon et al., 2008; Nostro et al., 2011; Rezania et al., 2012; Schulz et al., 2012; Xie et al., 2013). In contrast to normal islets or dispersed adult β cells, which release high levels of insulin in response to high levels of glucose in the “glucose stimulated insulin secretion” (GSIS) assay and can do so repeatedly, hPSC-derived insulin-expressing cells generated by existing methods fail to secrete insulin appropriately in response to the addition of various concentrations of glucose. Accordingly, there exists a need for a method of deriving cells from hPSCs which exhibit a phenotype of normal islets or mature adult β cells.